The ecosystem-level consequences of climate change-related range expansions are largely unexplored. In the Canadian Arctic, killer whale (Orcinus orca) occurrence is ice-restricted, and diminishing sea-ice cover has purportedly led to increased killer whale presence during the open-water season. However, the effects of increased predator presence on this Arctic marine ecosystem remain mostly unknown. In this thesis, I explore the consequences of such climate change-related predator range expansions. In chapter one, I review Canadian Arctic killer whale ecology and identify research priorities in the Canadian Arctic, two of which I address in chapters two and three. In chapter two, I whole-genome sequence twenty-nine western North Atlantic killer whales and describe two genetically distinct populations in Canadian waters: Canadian High Arctic and Canadian Low Arctic killer whales. Comparison with previously published genomes revealed Canadian High Arctic whales share a marginally significant excess of derived alleles with whales sampled in Newfoundland and Brazil, while Canadian Low Arctic whales share a significant excess of derived alleles with whales sampled in Greenland, Norway, and Iceland. In chapter three, I use photographs of sixty-three individually identifiable Canadian Arctic killer whales to estimate abundance in a capture-mark-recapture framework. The best-fitting model produced an estimate of 163±27, a number of killer whales which I determine could consume >1000 narwhal (Monodon monoceros) during their seasonal residency in Arctic waters. Collectively, these findings provide insight into the origins of Canadian Arctic killer whales and illustrate the magnitude of ecosystem-level modification that can occur with climate change-related shifts in predator distributions.